This is a symbol of the crucified wine god, Bacchus. Bacchus was the god of wine, fertility, and revelry in ancient Rome. The crescent moon and seven stars appear above the crucified figure of Bacchus. The original artifact that depicted this symbol came from Italy but was lost after World War II. The amulet is believed to be from the third century.
Ancient Romans threw Bacchanalia rituals that were large gatherings of women and men to celebrate Bacchus. For a time the Roman senate banned these rituals as they were considered too hedonistic.
The figure of Bacchus crucified could symbolize the withdrawal from the worship of Bacchus. The stars and crescent moon symbol above the god could symbolize a moon goddess from Roman times. The moon goddess symbolized fertility and womanhood in ancient Rome. Because Bacchus is crucified, this could be a symbol of a moon goddess cult that did not associate with Bacchus.